A microchannel is a channel prepared in a silicon dice, allowing a fluid to flow through. Among the preparation methods of the microchannel, an approach using a polysilicon sacrificial layer to define a microchannel was invented by Industrial Microelectronic Center (IMC) of Sweden, in 1997. According to this approach, a polysilicon sacrificial layer is prepared on a silicon substrate to define an area to be etched off. A low-stress silicon nitride (SiNx) layer is then formed on the sacrificial layer with the LPCVD (low-pressure chemical vapor deposition) technology. The silicon nitride layer is then etched with the RIE (reactive-ion etching) technology to produce a number of cavities in predetermined positions thereof. Thereafter, the assembly is etched in a KOH etchant such that the sacrificial layer is etched off. Then an area of the silicon substrate beneath the sacrificial layer is etched off to form a V-shape groove inside the silicon substrate. Finally the assembly is planarized by coating the upper surface of the SiNx layer with a silicon dioxide (SiO.sub.2) layer. A microchannel is thus prepared. IMC used this technology to produce flip chips for use in optical fiber passive alignment and in laser diodes.
A closed microchannel may also be prepared by bonding (positive pole bonding or by diffusion bonding) a glass substrate to a silicon substrate with a V-shape groove, or two silicon substrates both with a V-shape groove. If an element shall be prepared inside the microchannel, the sensor is formed on the planarization SiO.sub.2 layer, right up the V-shape groove. After the V-shape groove is prepared, the substrate containing such V-shape groove is bonded to another substrate to have a closed microchannel containing an element. This technology was disclosed by Honda in U.S. Pat. No. 5,620,929.
As described above, in the conventional art, the lower portions of the microchannel is prepared by etching the silicon substrate with an etchant from all directions. During the etching process, an area is reserved to deposit the sensor. When an open channel is prepared, the sensor is positioned on the reserved area. The assembly so prepared is then bonded with a glass substrate or another silicon substrate to have a closed microchannel. During the bonding process, pollution will be created and errors will be made. These and other factors are major reasons of decreased yield rate and high manufacture costs.
It is thus a need in the industry to have a new method to prepare a microchannel provided with an element whereby no bonding is needed in the preparation process.
It is also needed to have a method for the preparation of microchannel-sensor assembly where a microchannel and an element may be prepared in one process.
It is also needed to have a method for the preparation of microchannel-element assembly where planarization may be accomplished during the preparation of the assembly.